If all else fails, get a set of the decals you want in any size. Then scan them into your computer and use a photo editor (or in a pinch a word processor) to scale them to the size you want.

Do a test print on regular paper to be certain of the scale, then print them out on water slide decal paper. A word of advice - printers do not print white, so you you may need both white and clear decal paper. http://www.beldecal.com/ I have done this for many decals and have excellent results. For clear coating the decal, I have found that the following all work well and are good to 10% nitro or better - LusterKote clear, Ultracote clear and WATER BASE polyurethane.

Hope this helps.